GHSA-78g4-xqwv-q3g8

Pillow: Bundled libopenjp2 2.5.4 in all wheels since 11.1.0 carries OSV-2025-219 heap-buffer-overflow write reachable from Image.open().load()

Published

2026-10-22

Modified

2026-10-22

Sources

github-advisory

Summary

### Summary Every Pillow wheel from 11.1.0 onward bundles a libopenjp2 containing a heap-buffer-overflow **write** that is fixed upstream on master but has never appeared in an OpenJPEG release. See https://osv.dev/vulnerability/OSV-2025-219 Because the wheel bundles its own copy, a patched host OS does not help. It is reachable from `Image.open(fp); im.load()` with default settings. I am reporting it here rather than only upstream because Pillow is where the vulnerable binary actually reaches users. Note the inversion that makes this easy to miss: **OpenJPEG 2.5.2 and earlier are safe.** The bug was introduced in `954c6e3c` (2024-06-25), so keeping the dependency current is what creates the exposure. ### Details ## Affected wheels From `.github/dependencies.json` (`openjpeg`) at each tag: | Pillow | bundled OpenJPEG | status | |---|---|---| | 10.4.0 | 2.5.2 | safe | | 11.0.0 | 2.5.2 | safe | | **11.1.0, 11.2.1, 11.3.0** | **2.5.3** | **affected** | | **12.0.0 … 12.3.0** | **2.5.4** | **affected** | Confirmed on an installed wheel: `PIL.features.version_codec('jpg_2000')` → `2.5.4`, bundled file `pillow.libs/libopenjp2-*.so.2.5.4`. `main` still pins `2.5.4` as of 2026-10-06. ## The defect `src/lib/openjp2/j2k.c`, in `opj_j2k_read_sod`: ```c OPJ_UINT32 l_current_tile_part = l_cstr_index->tile_index[p_j2k->m_current_tile_number].current_tpsno; l_cstr_index->tile_index[...].tp_index[l_current_tile_part].end_header = l_current_pos; l_cstr_index->tile_index[...].tp_index[l_current_tile_part].end_pos = l_current_pos + p_j2k->m_specific_param.m_decoder.m_sot_length + 2; ``` `tp_index` is neither null-checked nor bounds-checked, and `l_current_tile_part` comes directly from the one-byte `TPsot` field of the SOT marker. The correct guard already exists a few lines later in `opj_j2k_add_tlmarker` (j2k.c:8459), writing the **same array at the same index** behind `if (tp_index && l_current_tile_part < nb_tps)`. One writer checked, its sibling not. Reached by giving the codestream a *valid* TLM marker — so `tp_index` is allocated once by `opj_j2k_build_tp_index_from_tlm`, sized to the TLM entry count, and `opj_j2k_read_sot` then skips all resizing — while setting `TNsot = 0` in every SOT, which keeps the TLM "valid" and lets `TPsot` walk past the allocation. ## Patch status Fixed upstream in `91d08b11` ("Fix heap buffer overlfow in opj_j2k_read_sod", 2026-02-10). The newest OpenJPEG tag is **v2.5.4 (2025-09-20)**, and `compare/v2.5.4...91d08b11` reports *ahead 6, behind 0* — the fix is **in no release, 8 months on**. ## Suggested remediation 1. Carry `91d08b11` as a patch in the wheel build until an OpenJPEG release includes it — three lines, identical to a guard already present in the same file. 2. Consider asking OpenJPEG to cut a release; they have had an unreleased memory-corruption fix on master since February 2026, and every distro is shipping the vulnerable code. 3. Your security handbook already tells applications to block EPS at the application layer. A similarly explicit note that `Image.open()` ignores filename/Content-Type and will reach any compiled-in codec unless `formats=` is passed would help downstream apps a lot. ## Not a Pillow bug, but relevant: the extension allowlist most apps rely on does not apply `Image.open()` sniffs magic bytes, so a JPEG 2000 codestream in a file named `avatar.png` declared `Content-Type: image/png` reaches the JP2 decoder anyway. I verified this against a production service documenting PNG/JPEG-only uploads: it accepted and fully decoded a JP2 through exactly that path, with 16 formats reachable from one upload endpoint against 43 registered openers. That service has since fixed it by passing `formats=` and validating on the detected format rather than the client's `Content-Type`. That is the reason a decoder-level issue like this one has much wider reach than downstream maintainers tend to assume. ### Proof of concept ASan build of OpenJPEG 2.5.4 interposed

Affected packages

Remediation: Upgrade to 13.0.0 or later.

References

• https://github.com/advisories/GHSA-78g4-xqwv-q3g8